566 BELL SYSTEM TECHNICAL JOURNAL 



apparatus cases containing these retardation coils installed in the cable 

 vault at West Unity, Ohio. 



In addition to this usage, retardation coils were installed in certain 

 instances in the conductors of branch cables and open wire taps. In 

 other branch cables and open wire taps w^here a higher degree of noise 

 current suppression was required the second noise suppression device 

 was used.^ This second device is a filter which provides a considerably 

 greater degree of suppression than the retardation coil. The purpose 

 of these is to attenuate longitudinal noise currents which might enter 

 the main cable over the conductors in the branch cable or open wire 

 tap. A typical installation of filters on aerial cable is shown by 

 Fig. 7-B. The question as to whether a retardation coil or a filter 

 was required in each particular case was determined by computations 

 of expected noise which might be contributed by the conductors 

 entering the main cable. This was done by considering the makeup 

 and length of the branch or tap, use to which it was put, and its 

 location with respect to the nearest carrier repeater input in the cable 

 to which it was connected. These computations, however, were made 

 coincidentally with those described earlier in determining the most 

 desirable directions of transmission. 



Five hundred fifty-one retardation coils and 132 filters were installed 

 in the 26 branch cables and open wire taps along the New York- 

 Charlotte route, 11 of which connect directly to open wire. On the 

 Detroit-South Bend project, 12 branch cables and open wire taps were 

 equipped with 44 retardation coils and 124 filters. Nine of the 12 are 

 taps connected directly to open wire. 



As a further step toward prevention of noise currents in the carrier 

 pairs, the shielding furnished by the lead sheaths of the cables has been 

 kept effective by maintaining continuous the electrical path through 

 these sheaths by means of shunts consisting of large condensers placed 

 across each insulating joint.'* 



Auxiliary Repeater Station Buildings 



Small buildings to house the auxiliary repeaters have been erected 

 at the sites determined to be acceptable from transmission and con- 

 struction standpoints. These structures are of fire resistive construc- 

 tion with concrete foundations, brick walls, and slate roofs. Since 

 these buildings house equipment which is expected to operate for long 

 periods of time without attention, no openings have been provided in 

 the walls except for an entrance door and ventilating units. Thermal 

 insulation has been provided over the ceiling. Two sizes of buildings 

 have been used. The larger one which is 24 ft. X 24 ft., inside dimen- 



